Paper No. 35
Presentation Time: 9:00 AM-6:30 PM
FINE-SCALE SPATIAL AND TEMPORAL VARIABILITY OF A TURRITELLA-RICH ASSEMBLAGE FROM THE JACKSON BLUFF FORMATION OF FLORIDA
The Plio-Pleistocene Jackson Bluff Formation of the northern Gulf Coast of Florida has been the focus of limited paleoenvironmental research in comparison to other formations of the Alum Bluff Group. In an effort to further constrain its geologic setting and depositional environment, a Turritella
-rich assemblage was examined in detail to better understand various elements of the depositional setting. The material examined was derived from a block collected from the Alum Bluff exposure on the Apalachicola River that measured 79 x 48 x 43 cm. Overall the assemblage was dominated by the bivalve Mulinia
, although locally, turritelline gastropods were the most abundant fossils present. The foraminifers represented include benthic taxa, largely Elphedium
, and Ammonia
, as well as relatively abundant freshwater gastropods. The above fossil assemblage in conjunction with the sedimentology supports the interpretation that this was a shallow environment, potentially brackish, with possibly high-nutrient levels due to riverine input; the most likely environment is that of an estuary.
An estuary setting presents the possibility of various types of potential riverine, tidal, or wave-driven currents affecting the physical placement of turritellines. The details of the Turritella orientation analysis displayed relatively random distributions with no clear relationship indicative of active uni- or bimodal currents associated with or soon after deposition. However, there was a distinct vertical-scale spatial variability in Turritella clusters that persisted unimpeded over time. Typically turritelline assemblages have been interpreted as products of upwelling, however, the data gathered from this assemblage and its association with an estuarine environment suggest that these types of associations can result from more than one mechanism.